In a simple and straightforward manner, Malkiel, author of A Random Walk Down Wall Street, and Mei, an economics professor at New York University, explain how to invest in emerging markets--that is, in firms based in countries where the per capita income is less than $9000 a year. The authors make a compelling case for taking advantage of the ""extraordinary opportunities"" afforded by such firms--their home economies are growing, their work forces are becoming better educated and modern technology levels the playing field. Malkiel and Mei also suggest how to hedge your bets when investing in such high-risk markets: e.g., limit those stocks to 30% of your total portfolio and rely on professional managers and index funds where possible. And although they recommend against it, the authors even explain how to construct an emerging-market portfolio. Illustrations. (Jan.)